The invention relates to well isolation systems.
In a wellbore, one or more valves may be used to control flow of fluid between different sections of the wellbore. Such valves are sometimes referred to as formation isolation valves. A formation isolation valve may include a ball valve, a flapper valve, or a sleeve valve that is controllable to open or shut sections of the well.
In wells with multiple completion zones, valves are also used to isolate the different zones. Typically during completion of multiple zone wells, a first zone is perforated using a perforating string to achieve communication between the wellbore and adjacent formation and the zone may be subsequently completed. If completion of a second zone is desired, a valve may be used to isolate the first zone while the second zone completion operation proceeds. Additional valves may be positioned in the wellbore to selectively isolate one or more of the multiple zones.
In a selective zone completion where flow from each zone is flowed and controlled individually, the individual zones are separated by flow tubes. These flow tubes may have to be passed through the valves in an upstream zone to access a downstream zone. To do so, the valves are opened; for example, if flapper valves are used, they are broken by applied pressure or some mechanical mechanism so that the equipment may pass through the upstream zone to the downstream zone. Once the flapper valve is broken, however, the upstream zone is unprotected and the well may start taking fluid until the equipment has been run to and set in the downstream zone. Because zones may be large distances apart (e.g., thousands of feet), the time for the equipment to traverse the distance between the zones may be long, especially if relatively sophisticated equipment such as those in intelligent completion systems are used.
During this time, fluid pressure from the first zone is monitored to detect sudden fluctuations in well pressure which may cause a blowout condition. If well control is required, such as by activation of a blowout preventer (BOP), closing the BOP on tubing which may have cables, flat packs, and hydraulic lines attached to the outer surface of the tubing may damage the attached components and the BOP may not seal properly.
Thus, an improved isolation system is needed that reliably provides fluid control in a well.